Circadian-rhythmic variations of biochemical parameters in the yearlings of indigenous perch (Perca fluviatilis L.) and nonindigenous tyulka (Clupeonella cultriventris Nordmann) from the Rybinsk Reservoir (Russia)

Diurnal variations of some parameters of protein, lipid, and water metabolisms in the underyearlings of indigenous (perch, Perca fluviatilis L.) and nonindigenous (tyulka, Clupeonella cultriventris Nordmann) fish species have been analyzed. These species form the basis of feeding aggregations of young fish in the Rybinsk Reservoir pelagial. No significant daily fluctuations in the values of protein content, water, and lipids in the studied fish species were revealed. Stable interspecific differences in mean daily and hourly values of the above-mentioned components, as well as in the contents of three lipid fractions—phospholipids (PLs), free cholesterol (FC), and triacylglycerols (TAGs)—have been determined at the level of whole organism. It is shown that the level of adipose reserves and the content of TAG in the tyulka are higher than in perch, while the contents of proteins, PL, and FC are lower. Diurnal variations of the level of each of the three fractions in both fish species are similar, but the ranges of variations are wider in tyulka than in perch. Possible mechanisms for the regulation of lipid metabolism and their similarity in young fish of different species upon adaptation to short-term changes in the environment are discussed. It is suggested that the modern state of the zooplankton community in the Rybinsk Reservoir pelagial negatively affects the feeding of perch underyearlings and parameters of lipid metabolism in their organisms.     

Specific features of feeding in underyearlings of zander (<Emphasis Type="Italic">Sander lucioperca</Emphasis>) (Percidae) of the Rybinsk reservoir in various years

The results of the studies on feeding of zander (Sander lucioperca) underyearlings in the Rybinsk Reservoir in 2008-2010 and 2012 are presented. The study revealed that, at feeding on plankton, the assemblage of the organisms consumed by juvenile zander has not been changed compared to 1950. The underyearlings prefer to feed on large zooplankters—Daphnia longispina, Leptodora kindtii, and Bythotrephes longimanus—along with copepods. At some sampling stations, the species of macrozoobenthos were included in the young zander food. The piscine component of zander food was dominated by underyearlings of Azov-Black sea tyulka (Clupeonella cultriventris); the fries of perch (Perca fluviatilis) and cyprinids (Cyprinidae) were less important. The feeding strategy of zander underyearlings was unchanged in various years. At turning to predatory feeding, not only the ratio of sizes of predator versus prey but also the proportion of the densities of their populations plays an important role.     

On the diurnal rhythm and feeding electivity in kilka (<Emphasis Type="Italic">Clupeonella cultriventris</Emphasis>) in Rybinsk Reservoir

Diurnal rhythms, feeding electivity, and feeding resources were studied for the new for Rybinsk Reservoir fish species, kilka (Clupeonella cultriventris). It is revealed that, in Rybinsk Reservoir, kilka actively feeds during day time. Selective feeding is a characteristic of this fish. Yearlings prefer small Cyclopoida and their young specimens dominating in zooplankton. Two-year-old fish actively select innumerous but large crustaceans of genera Heterocope, Bythotrephes, Leptodora, and Cyclops. Possible factors determining selection of food items by kilka are discussed. These factors are as follows: zooplankters’ biomasses, the extent of plankters’ aggregations, body size, and visibility of some prey species for kilka (as determined by movement pattern, transparency and cuticle color, presence of eggs, or large eye).     

The lipid status of young of the year mykiss <Emphasis Type="Italic">Parasalmo mykiss</Emphasis> and coho salmon <Emphasis Type="Italic">Oncorhynchus kisutch</Emphasis>

The young of the year mykiss Parasalmo mykiss and coho salmon Oncorhynchus kisutch which perform downstream migration and which stay in the coastal zone during the period of primary dispersion represent different phenotypic groups. They differ in weight, length, and lipid status. Such differentiation is a factor controlling the formation of intrapopulation diversity and of the life strategy of fish. It may determine the timing of smoltification in the future and, further on, of the return for spawning. There were found some analogies and differences in characteristics of lipid metabolism in the investigated species. The content of total lipids decreases by autumn in underyearlings of both species. Furthermore, changes in the content of particular lipid fractions are multidirectional and various scaled, seemingly being related to physiological preparation for the wintering.     

The role of kilka (<Emphasis Type="Italic">Clupeonella cultriventris</Emphasis> (Nordmann)) in the diet of predatory fish of the Rybinsk reservoir

Data on predator fish feeding in the Rybinsk reservoir in the first years (2000–2003) of Ponto-Caspian kilka expansion are given. It is shown that the kilka’s penetration into the Rybinsk reservoir caused changes in the feeding spectra of predator fish. Kilka became one of the main objects of predator feeding throughout the whole year. In the open water period, it is consumed by pikeperch Stizostedion lucioperca (Linnaeus) and Volga pikeperch Stizostedion volgense (Gmelin) in the pelagial and by pike Esox lucius Linnaeus and perch Perca fluviatilis Linnaeus in the sublittoral and shallow bays. In winter it is mostly eaten by burbot Lota lota (Linnaeus) and pikeperch.     

Circadian rhythmic changes in the lipid composition of muscles in kilka <Emphasis Type="Italic">Clupeonella cultriventris</Emphasis> (Clupeidae,clupeiformes) during natural periodicity of feeding in the feeding and spawning periods in the Rybinsk Reservoir

According to data of observations in 2002–2004, differences in the pattern of diurnal fluctuations in the total content and fractional composition of lipids in muscles of mature specimens of kilka Clupeonella cultriventris from the Rybinsk Reservoir in the feeding and spawning periods were revealed. It was established that the feeding intensity in kilka considerably changes throughout 24 h in both periods of the annual cycle, while diurnal fluctuations in the fatness of muscles are distinctly manifested only in the reproductive period and have a dissimilar pattern in specimens of different sexes. In females and males, they are determined mainly by the change in the content of the fraction of reserve lipids-triacylglycerols, as a rule, by its increase in the light hours of the day, several hours after an increase in the feeding activity of fish. The pattern of diurnal fluctuations of the level of lipid fractions (phospholipids, triacylglycerols, cholesterol, and its ethers) in kilka’s muscles differs from that in the feeding period. Possible causes of the change of diurnal variations of the considered indices of lipid metabolism in kilka at an increase in the endocrine activity of its body in the reproductive period is discussed.     

The lipid status and feeding habits of yearlings of mykiss <Emphasis Type="Italic">Parasalmo mykiss</Emphasis> and coho salmon <Emphasis Type="Italic">Oncorhynchus kisutch</Emphasis> in autumn

Juveniles of coho salmon Oncorhynchus kisutch and mykiss Parasalmo mykiss at the age 1 + (yearlings) are differentiated by the content of different fractions of lipids (the lipid status), feeding habits, and by size-weight characteristics even eight months prior to smoltification. The juveniles of coho salmon and mykiss with high lipid status consume more calorific food items and, as a rule, have higher (on average) body length and weight. The juveniles with low lipid status consume less calorific organisms and have lower body length and weight. It is supposed that a considerable part of juveniles with high lipid status will migrate seaward the next year. The role of feeding habits in formation of this differentiation and, accordingly, in determination of timing of smoltification are discussed.     

Sexual Dimorphism of Physiological and Biochemical State of Trunk Muscle in Bleak (<Emphasis Type="Italic">Alburnus alburnus</Emphasis> L.) (Cypriniformes,Cyprinidae) Spawners of the Rybinsk Reservoir in the Prespawning Period

The sexual dimorphism of physiological and biochemical parameters of trunk muscle in bleak spawners, representatives of an abundant nonexploited fish species of the Rybinsk Reservoir, has been analyzed in the prespawning period. Sex-related differences in the overall biochemical and lipid composition of trunk muscle and in muscle composition variability in age- and size-matched individuals have been assessed. The distribution of trunk-muscle lipid content is bimodal in females and unimodal in males. The variability of muscle lipid parameters in the aggregated samples is higher in females than in males. The putative reasons for the distinctive features of physiological and biochemical parameters of muscle tissue detected in bleak of different sexes in the prespawning period are discussed.     

Diurnal vertical migrations of bream <Emphasis Type="Italic">Abramis brama</Emphasis>

According to trawl-acoustic surveys, differences in the range of diurnal vertical movements of bream Abramis brama in the Rybinsk and Ivankovo reservoirs are revealed. The observed fish behavior is related to strategy of occupation of feeding biotopes. It is supposed that residence in bottom payers under conditions of low temperature is oriented to energy saving.     

On the physiological-biochemical state of kilka Clupeonella cultriventris (Clupeidae, Clupeiformes) in Rybinsk Reservoir (Russia)

The results of studies into lipid total content and fractional composition in the tissue and wholebody levels in kilka (Clupeonella cultriventris) are given. The fish studied belonged to various size-age groups and were sampled in Rybinsk Reservoir during active feeding periods in 2002 and 2005. A trend was revealed of deterioration of the physiological-biochemical state in adult specimens of this invasive species. This was especially true of the modal (in terms of their proportion in population) two-year-old fish. This was evidenced by a decrease in contents of total and reserve (triacylglycerol) lipids in fish muscles during the whole study period. It is shown that, in young kilka caught in all reservoir stretches in autumn, the values of these parameters depend on the time and rate of the reservoir water level decrease during the active feeding period. Probable reasons for changes in the physiological-biochemical state in adult and young specimens in the kilka population are discussed. The discussion is in view of the recent state of the Rybinsk Reservoir ecosystem which undergoes successional modification of the pelagic zooplankton community both at the level of large taxa and of some dominant species.     

Comparative analysis of the indices of immunophysiological state in bream (<Emphasis Type="Italic">Abramis brama</Emphasis> (L.)) from parts of the Rybinsk Reservoir with different extents of pollution

The indices of the cellular and humoral components of natural immunity in bream from parts of the Rybinsk Reservoir with different extents of contamination are studied. Considerable differences were revealed in a range of parameters between the fish sampled in the Sheksninskii reach, which receives waste-waters from the Cherepovets industrial center, and the fish from the relatively unpolluted Molozhskii reach. An analysis of the data shows evidence for the active state of the mechanisms of nonspecific resistance in the fish from polluted sites.     

Feeding of juvenile sterlet (<Emphasis Type="Italic">Acipenser ruthenus</Emphasis>, Acipenseridae) in the Danube River midstream

The present paper provides the results of the study on feeding of juvenile (underyearlings and age 2+) sterlet (Acipenser ruthenus) caught in the Danube River in 2002–2003. The full spectrum of food items found in the fish stomachs was identified. The seasonal patterns of food composition are revealed. It is shown that juvenile sterlet in the Danube feeds mainly on larvae of chironomids and trichopterans, amphipods, and leeches. The organisms typical for lithophilic and lithorheophilic biocenoses play considerable role in the feeding of sterlet. Mean daily gains of body length and weight in the sterlet underyearlings are calculated.     

Variation of food spectra of tube-nosed goby <Emphasis Type="Italic">Proterorhinus marmoratus</Emphasis> (Perciformes,Gobiidae)—a new species in the Rybinsk Reservoir

Size-age structure and food composition of tube-nosed goby Proterorhinus marmoratus in the Rybinsk Reservoir have been studied. It was shown that food spectra changed in the process of dispersal of this species over the water body and considerably vary during the season. In the period of naturalization, feeding of the tube-nosed goby is characterized by group specialization; the object of specialization is Gmelinoides. Having dispersed over the water body and naturalized, it manifested itself as a generalist; its food composition became diverse and was determined by the seasonal dynamics of the population and biomass of food items.     

Assessment of Possible Causes of Changes in Аbundance and Sexual Structure in Populations of Prussian Carp (<Emphasis Type="Italic">Carassius auratus gibelio</Emphasis> Bloch., 1783)

The prevalence of processes of the increase in abundance and changes in the sexual structure of Prussian carp populations in waterbodies differing dramatically in ecological properties and distant from each other (Lake Sevan and Rybinsk Reservoir) indicates the presence of global factors affecting climatic zones. The increase in environmental temperature due to global warming may be such a factor. Experimentally proven high thermophilicity and the thermal stability of Prussian carp, as well as its low sensitivity to hypoxia, provide some advantages for this species over many other fish inhabiting the same waterbodies.     

Functional state of the liver antioxidant system of the bream <Emphasis Type="Italic">Abramis brama</Emphasis> (L.) from Rybinsk Reservoir regions with different anthropogenic loads

The breams living in five regions of the Rybinsk Reservoir with different degrees of anthropogenic load have been assayed for the characteristics of their antioxidant system (AOS) and lipid peroxidation (LPO) system. Individuals caught at two stations in the Rybinsk Reservoir that maximally differ in the degree of pollution display different qualitative and quantitative compositions of polychlorinated biphenyls (PCBs). At the station at the Sheksninskii Reach, which is located near a local source of pollution (Cherepovets), the total content of PCBs and homologous groups of congeners is one order of magnitude higher than in the bream living at the station of the comparatively clean Molozhskii Reach. The AOS response and the generation intensity of LPO products in the bream (Abramis brama L.) liver caused by different degrees of anthropogenic pollution have been determined. The content of LPO products in the liver of the breams caught in the Sheksninskii Reach is considerably higher and the values of AOS characteristics are considerably lower than in the fish from the Molozhskii Reach. The bream living in the Molozhskii and Volzhskii Reaches are in a more favorable state than those in the Sheksninskii Reach. The AOS and LPO characteristics are an appropriate biomarker for estimating the state of the health of the fish.     

Feeding behaviour determining differential capture success of evasive prey in underyearling European perch (<Emphasis Type="Italic">Perca fluviatilis</Emphasis> L.) and roach (<Emphasis Type="Italic">Rutilus rutilus</Emphasis> (L.))

The effect of feeding behaviour on the prey capture efficiency of young-of-the-year European perch and roach was investigated in laboratory experiments using planktonic crustaceans possessing different escape abilities—Daphnia sp. and Cyclops sp. Two sets of experiments were performed. In the first set, the feeding efficiency and behaviour of 270 fish individuals were determined by stomach content analyses and video record evaluations. In the second set of experiments, analysis of attack-effort, which was evaluated as attack-distance and repeated strikes, was undertaken. Except for situations in which Daphnia was offered at high densities, the feeding efficiency of perch was significantly higher compared to roach in all other combinations of prey types and densities. Roach consumed significantly less prey compared to perch when feeding exclusively on the evasive Cyclops and when it was offered in a 1:1 ratio mixture with Daphnia. The mean swimming speed was similar in both fish species, but behavioural differences were evident during prey search and capture. Perch swam through the aquaria in short and fast movements that were interrupted by many stops. Roach exhibited rather continuous swimming that was punctuated by slowdowns instead of stops. The perch attacks were very intensive and repeated strikes occurred, particularly when feeding on evasive Cyclops. On the other hand, roach revealed strong schooling behaviour restricting the fish during inspection of the experimental aquaria. The distinct differences in feeding efficiency between perch and roach were demonstrated to be closely related to differences in their feeding behaviour. Discontinuous searching for prey, vigorous attacks, occurrence of repeated strikes and the absence of schooling increased perch prey capture efficiency, particularly when foraging on evasive copepods.     

Morphological Variability of Roach <Emphasis Type="Italic">Rutilus rutilus</Emphasis> (L.) from the Volga Reach of Rybinsk Reservoir

A comparative analysis of literature data and our own results on the morphology of roach from the Volga Reach (Rybinsk Reservoir) in different years is conducted. Recently, (from 2007 to 2010), the morphological characteristics of the roach have been similar to those observed between 1976 and 1978. The roach is characterized by an intermediate position between the herbivorous and malacophagous morphs, but it is more similar to the herbivorous morph.     

Role of phospholipids in early ontogenesis of Arctic-Boreal species <Emphasis Type="Italic">Leptoclinus maculatus</Emphasis> (Stichaeidae)

The content of total phospholipids and their classes (phosphatidylinositol, phosphatidylserine, phosphatidylethanolamine, phosphatidylcholine, sphingomyelin) of muscles (flesh) and lipid sac of different developmental stages of young fish the daubed shanny, Leptoclinus maculatus from Kongsfjord (Svalbard, Norway) in winter was studied. The content of phospholipids in flesh decreases with age on account of phosphatidylcholine and phosphatidylethanolamine that probably related to their role in morphogenesis during differentiation of tissues and organs. The content of phospholipids is lower than reserve lipids in the lipid sac. The level of phospholipids in the lipid sac compared to flesh increases with age of fish reaching the maximum in benthic juveniles. Variations of minor phospholipids content of young fish of the daubed shanny indicate their participation in biochemical mechanisms of adaptation realizing in specific and varying Arctic conditions.     

Ethanol Metabolism in the Yeasts <Emphasis Type="Italic">Yarrowia</Emphasis> and <Emphasis Type="Italic">Torulopsis</Emphasis>: A Review

Results of research into ethanol metabolism in yeast organisms with highly pronounced aerobic metabolism are reviewed. The low activity of NAD-dependent alcohol dehydrogenase (EC 1.1.1.1), observed under conditions of aerobic yeast growth on ethanol, demonstrates that alternative enzyme systems—alcohol oxidase (EC 1.1.3.13), microsomal ethanol-oxidizing system (including cytochrome P-450), and catalase (EC 1.11.1.6)—may be involved in the alcohol oxidation. The role of these systems in alcohol oxidation and the conditions favoring their operation in this processes are analyzed. It is concluded that iron ions are important regulators of ethanol metabolism for the microorganisms of this group.     

Interspecific differences in drift behaviour between the native <Emphasis Type="Italic">Gammarus pulex</Emphasis> and the exotic <Emphasis Type="Italic">Gammarus roeseli</Emphasis> and possible implications for the invader’s success

“Drifting” is known to subject aquatic invertebrates to intense predation by drift feeding fish. Consequently, interspecific variations in drifting behaviour could lead to differences in predation pressure between coexisting prey species. Predation being an important factor determining the success of invaders, differences in drift patterns could advantage either native or exotic invertebrates through differential predation by native fish predators. The exotic freshwater amphipod (Gammarus roeseli) has now largely colonized Western Europe where it is often found in sympatry with a native species (Gammarus pulex). Here we documented interspecific differences in drifting behaviour that might have favored the invader’s success through differential predation. Benthic and drifting amphipods were sampled three times at the same site to compare the proportion of each species within and between sample types (benthos or drift) across time. Compared with the benthos, where the invader (G. roeseli) was significantly less abundant than the native (G. pulex), G. roeseli was proportionally overrepresented in the drift but displayed a very different drifting pattern. While G. pulex drift rates remained roughly constant over a 24 h period, G. roeseli showed a marked diel periodicity with low diurnal and high nocturnal drift rates. Such drifting behaviour could procure this species with a competitive advantage regarding predation as most drift feeding fish are diurnal. As a result, the native appears more disadvantaged with respect to drift. This may partly explain the ability of G. roeseli to coexist with G. pulex in a habitat more suitable to the native.